This inention relates to a combustor for fine particulate coal, a plentiful fuel in the United States. Coal can be used as a fuel to provide a stream of clean, hot gas for a prime mover such as a gas turbine in, for example, a peaking station for generation of electricity or a locomotive. However, because coal is a solid, its use as a fuel creates ash and soot as well as the usual pollutants resulting from combustion. Turbine blades are quite vulnerable to erosion by particulates in the gas stream, and can also be corroded by chemical reactions occurring between matter in the gas stream and the blade metal at the high temperature at which the turbine is operating. These processes together can destroy a turbine blade in a very short time. Thus, it is important that the gas stream be free of particulate matter.
Using finely ground coal allows a combustion process resulting in a clean stream of hot gas. However, while combustion of fine particulate reduces ash, the combustion process can be difficult to control. Combustion must occur in a manner which insures good control of the temperature and the local and overall stoichiometric ratio (the ratio of air to fuel in the mixture) to insure complete combustion, and avoid formation of nitrogen oxide, a pollutant, as well as soot, which is extremely difficult to burn. If the temperature is too high, the formation of nitrogen oxides is encouraged; if it is too low, combustion is incomplete and soot will be formed. A local excess of air per unit of fuel likewise leads to formation of nitrogen oxides; a deficiency results in localized incomplete combustion and production of soot. Of course, both are undesirable since nitrogen oxides pollute the atmosphere, and soot prevents the delivery of clean gas.